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Question about DHCP leases

I find that my router waits until the entire lease time passes before renewing, but when I power up my CentOS VM with a dhcp server running and I connect it to the WAN port on my router, my router will follow RFC guidelines and renew when half of the lease time passes. My question is what is my ISP's dhcp server doing to have my router wait until the lease expires before renewing?


  • mfillpotmfillpot Posts: 2,180
    Your question is confusing me a little bit. It is that the router is not renewing the WAN connection in the right intervals or that the host (possibly windows) is not renewing the lease from the router in the right time frame. And are you referring to CentOS being used as a service or client to dhcp?
  • It's the router that's not renewing the WAN connection in the right intervals when it obtains a lease from the ISP (waiting up until the lease expires to renew). I was using CentOS as a dhcp service (not client) to figure out if it was an issue with the router itself or is it something the ISP's dhcp server is doing that's telling my router to wait the entire lease before renewing(When I did this scenario the router only waited until half of the lease time passed before renewing, as it should.)
  • mfillpotmfillpot Posts: 2,180
    It sounds like the ISP or their manufacturer modified the source code the dhcp client on the router to change the renewal rules, most likely to limit calls to their dhcpd daemon.
  • But why does it comply with RFC when I set it up to obtain a lease from the dhcp service on my CentOS virtual machine? That's what's puzzling me.

    FYI, the ISP did not provide me with the router.
  • mfillpotmfillpot Posts: 2,180
    IF the router is properly following the RFC standards then the problem may be that the ISP DHCP server could also be denying the renewal requests if they are received before the termination. However it works you were able to eliminate the router as the cause of the problems, so we can only guess why the ISP has changed the renewal period.
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